1. Field of the Invention
The present invention relates to an intake system for a multi-cylinder engine.
2. Description of Related Art
Recently, there is the increasing tendency that combustion engines can achieve dynamic effect of intake air, for example, that they perform inertia supercharging. The inertia supercharging is performed by using a surge tank, as a pressure-reversing portion where the pressure is reversed, by connecting the surge tank individually and independently to each of the cylinders through the independent intake passages. The longer the length of the independent intake passages from the respective cylinders to the pressure-reversing portion, the lower the number of revolutions of the combustion engine for supercharging in synchronism with inertia.
For instance, Japanese Patent Laid-open Publication (kokai) No. 210,219/1987 proposes an intake system in which supercharging be performed in synchronism with inertia in both a low rotation region of the combustion engine and a high rotation region thereof by switching between a relatively short intake passage and a relatively long intake passage, thereby providing the combustion engine with high and flat output torque over a wide rotation range. In such a case, it is also proposed that plural volume chambers having intake passages of different lengths between the respective volume chambers and intake ports are provided and the volume chamber is so chosen as to correspond to the number of revolutions of the combustion engine and as to be employed as a pressure-reversing portion.
It is also the growing tendency that supercharging is performed in synchronism with resonance in order to gain the dynamic effect of intake air. In order to perform the supercharging in synchronism with resonance, cylinders are so set as to allow their intake strokes to be not adjacent each other and such cylinders are combined into a group. Further, plural groups of such cylinders are provided and, for each group of the cylinders, each of the cylinders is connected individually and independently to the volume portion, such as the surge tank, through the respective independent intake passages and the volume portion for each of the groups of the cylinders are communicated to each other through a passage causing resonance.
In either case where supercharging is performed in synchronism with inertia or where supercharging is performed in synchronism with resonance, a predetermined volume portion is required. This volume portion, however, is so considerably large in volume and size that such a large volume of the volume portion presents the problem that the intake system is made compact and eventually the combustion engine is made compact as a whole.